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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - OMNICS (Observing, Modelling and Predicting in situ Petrophysical Parameter Evolution in a Geologic Carbon Storage System)

Teaser

Summary

Geologic carbon storage is one of the most promising options for decreasing atmospheric CO2 but a major challenge is how to control the distribution of supercritical CO2 in evolving porous rock formations. In many cases, natural, fluid distributing systems are remarkably efficient in dissipating or collecting fluids because of the interaction between the fluids and hierarchical assemblages of complex microstructures. These structures are difficult to design and fabricate artificially, because we do not know how the enormous number of small features are generated and assembled autonomously. My aim is to determine the relationships between global constraints and the evolution of internal structures in fluid distributing systems, particularly in the context of geologic carbon storage. The research will create synergy between in situ X-ray tomography (CT) and a reactor network model. CT can be used to monitor the evolution of structures; modelling helps assemble knowledge and analyse the importance of variables. On the short term, the results will provide base information to policy makers for informed decisions about how to tackle global warming and on the long term, through the development of the synergetic technologies, will contribute to the design of advanced energy and medical materials.

Upon conclusion, OMNICS delivered a toolset for investigating the microstructure evolution of geomaterials under geologic carbon storage (GCS) conditions. The toolset consists of three components: a sample environment for in situ X-ray imaging of flow through experiments, a conceptual model for microscopic pore development and a numerical simulation programme for predicting structural changes of porous media in a flow field. Two fluid cells have been manufactured and are fully functional with both synchrotron beamlines and benchtop tomography (CT) systems. A reactor network model has been built to conceptualise the different aspects of a coupled flow-reaction process and deployed on parallel computing systems for numerical simulations. The results of OMNICS have led to seven manuscripts documenting the technical details of each tool and the scientific discoveries enabled by the use of the toolset.

Work performed

- Two fluid cells have been built according to a design that functions under 250 bar of pressure and up to 90 oC of temperature. The fluid cells are miniatures of Hassler core holders, which host various sizes of rock samples and can be mounted to the rotating stage of a tomography facility.
- The fluid cell has been successfully tested in various tomography facilities for in situ X-ray imaging. The national facilities include: Deutsches Elektronen-Synchrotron (DESY), Super Photon ring-8 GeV (SPring-8), the Swiss Lightsource (SLS) and Swiss Spallation Neutron Source (SINQ) of Paul Scherrer Institut (PSI) and European Synchrotron Radiation Facility (ESRF). The fluid cell has also been used as sample environment in a variety of Nikon and Zeiss (Xradia) benchtop CT systems, located at the Danish Technical University (DTU) and the Manchester X-ray Imaging Facility (MXIF).
- The fluid cell was used to study chalk microstructure evolution under circumneutral condition with full flow field imaging. The dataset provided the basis for a discussion regarding the transient DamkÃ¶hler space in a flow field imposed on natural porous media.
- The fluid cell was used in a region of interest (ROI) imaging setup to monitor highly localised pore structure development in acidic environments. The dataset provided the basis for a discussion on the path selection of wormhole growth in geologic materials.
- The fluid cell was also used with full field imaging to study the evolution of geometric surface in chalk under GCS relevant conditions. During that experiment, we recorded a highly counterintuitive phenomenon: the aqueous reactant migrated against the flow direction due to a momentarily increased reactive surface area. The resulting manuscript initiated an extensive discussion regarding the definition of â€œsurfaceâ€ in both the imaging and the geophysics community.
- Two versions of reactor network model have been developed:
a. The first version is a 3D model that is optimised to use with greyscale X-ray tomography and to predict the evolution of chalk microstructure given the knowledge of geochemical kinetics. This version has been polished to the extent that a decent workstation (desktop computer) can handle a network of 100 million reacting entities. It has been used to predict structural changes as well as to validate and interpret in situ experimental observations.
b. The second version is a 2D model with a coordination number of 6. This model has been a happy accident (it was not planned in the OMNICS proposal). It will be an important numerical tool to study the branching morphogenesis in both hydrologic and biologic systems in the researcherâ€™s future academic career.
- The reactor network model also led to a reinvention of the segregated flow model (SFM) in hydrology. SFM has been used to quantify the performance of chemical reactors before the popularisation of computers. The researcher was inspired by the reactor network model and developed the mathematical theory behind a new application of SFM. In this application, the phenomenological correlation between dissolution kinetics and fluid composition in a closed, free drift system can be used to predict the reactant gradients in a flow field. This transformation, from a system with an infinitely long residence time to a system with a finite residence time, was enabled through exploiting the mathematical similarity between the governing equations of a batch reactor and a plug flow reactor.
- Seven manuscripts; all preprints deposited on arxiv.org and are openly accessible.

Final results

Overall, the project has been both fruitful and enjoyable for the researcher. The positive impact of OMNICS will drive the researcher to make concrete and long term contributions to the scientific community. The researcher has embarked on the next career step, working towards setting up a laboratory for branching morphogenesis research. The conceptual model of the future research was nurtured during OMNICS. OMNICS addressed an issue related to the environment and climate change, whereas the new research direction will not only push further on this issue but also use the knowledge of hydrologic branching structure to help manufacture artificial tissue and organs. The new research is expected to have a substantial impact on both medical and geo- engineering, by alleviating the worldwide, unmet need for human tissues and organs and by bridging the huge knowledge gap between geology and biology.

As a fundamental research project, the long term impact of OMNICS on the related scientific communities is subject to public scrutiny and will not be clear until a few years later. However, the researcher is confident to say that the reactive transport modellers in various disciplines are all potential users of the new methodologies that came out from OMNICS. They will benefit from having more options in tackling problems.